U.S. patent number 11,245,348 [Application Number 16/811,260] was granted by the patent office on 2022-02-08 for method for controlling a long-stator linear motor.
This patent grant is currently assigned to B&R INDUSTRIAL AUTOMATION GMBH. The grantee listed for this patent is B&R INDUSTRIAL AUTOMATION GMBH. Invention is credited to Alexander Almeder, Stefan Flixeder, Stefan Huber.
United States Patent |
11,245,348 |
Flixeder , et al. |
February 8, 2022 |
Method for controlling a long-stator linear motor
Abstract
In order to improve control of a long-stator linear motor, a
first measured value is ascertained in a first measurement section
and a second measured value is ascertained in a second measurement
section, in each case along a transport path in a movement
direction. The first measurement section overlaps, in the movement
direction, the second measurement section in an overlap region, and
the first measured value and the second measured value represent
the same actual value of a physical quantity. An operating
parameter of the long-stator linear motor determined based on a
deviation occurring between the first measured value and the second
measured value.
Inventors: |
Flixeder; Stefan (Eggelsberg,
AT), Huber; Stefan (Eggelsberg, AT),
Almeder; Alexander (Eggelsberg, AT) |
Applicant: |
Name |
City |
State |
Country |
Type |
B&R INDUSTRIAL AUTOMATION GMBH |
Eggelsberg |
N/A |
AT |
|
|
Assignee: |
B&R INDUSTRIAL AUTOMATION
GMBH (Eggelsberg, AT)
|
Family
ID: |
1000006102872 |
Appl.
No.: |
16/811,260 |
Filed: |
March 6, 2020 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
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US 20200287493 A1 |
Sep 10, 2020 |
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Foreign Application Priority Data
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Mar 7, 2019 [EP] |
|
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19161181 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02P
25/064 (20160201); G01R 31/343 (20130101) |
Current International
Class: |
H02P
25/064 (20160101); G01R 31/34 (20200101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 860 496 |
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Apr 2015 |
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EP |
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3 251 986 |
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Dec 2017 |
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EP |
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3 367 068 |
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Aug 2018 |
|
EP |
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2014-196940 |
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Oct 2014 |
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JP |
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2008/072525 |
|
Jun 2008 |
|
WO |
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WO2008072525 |
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Jun 2008 |
|
WO |
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Other References
Hiller, "Ferraris Acceleration Sensor--Principle and Field of
Application in Servo Drives", Hubner Elektromaschinen AG, Berlin,
Germany, downloaded from Internet: URL:https://pdfs.
semanticscholar.org/ecfb/5b98a45473797e8e47f09f
8f0c8a50f4bbdl.pdf?ga=2.15626614.1718334140.1567668397-330839178.15675216-
26 [downloaded on Sep. 5, 2019] , Dec. 30, 2003, pp. 1-6. cited by
applicant .
Official Communication issued in European Patent Office (EPO)
Patent Application No. 19161181.3, dated Sep. 5, 2019. cited by
applicant.
|
Primary Examiner: Imtiaz; Zoheb S
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Claims
The invention claimed is:
1. A method for controlling a long-stator linear motor, by a first
measured value being ascertained in a first measurement section and
a second measured value being ascertained in a second measurement
section, in each case along a transport path in a movement
direction, wherein the first measurement section overlaps, in an
overlap region in the movement direction, the second measurement
section, wherein the first measured value and the second measured
value represent the same actual value of a physical quantity, and
wherein an operating parameter of the long-stator linear motor is
determined based on a deviation occurring between the first
measured value and the second measured value.
2. The method according to claim 1, wherein the measurement
sections are provided on opposite sides of the transport path.
3. The method according to claim 1, wherein the measurement
sections are provided on the same side of the transport path.
4. The method according to claim 1, wherein an approximation of the
actual value is determined as the operating parameter.
5. The method according to claim 4, wherein the first or the second
measured value is selected as an approximation of the actual
value.
6. The method according to claim 4, wherein the first or the second
measured value is selected based on a classification of the
respective measured values.
7. The method according to claim 5, wherein the first or the second
measured value is selected based on an expected accuracy of the
respective measured values.
8. The method according to claim 4, wherein each of the first and
the second measured value is provided with a weighting factor, and
wherein the approximation of the actual value is ascertained as the
operating parameter from the first and the second measured value
and from the associated weighting factor in each case.
9. The method according to claim 8, wherein the weighting factor
comprises a model factor which is determined by the magnitude of a
deviation of the associated measured value from a reference
model.
10. The method according to claim 8, wherein the weighting factor
comprises a geometry factor which is determined by the position of
the relevant measured value in the associated measurement
section.
11. The method according to claim 8, wherein the weighting factor
comprises a statistical factor which is determined by a statistical
distribution function.
12. The method according to claim 1, wherein the occurrence of
interference and/or an error and/or wear on the long-stator linear
motor is determined as the operating parameter.
13. The method according to claim 1, wherein in each case a
position of a transport unit on the transport path is ascertained
as the first and the second measured value.
14. The method according to claim 1, wherein in each case a speed
and/or an acceleration of a transport unit on the transport path is
ascertained as the first and the second measured value.
15. The method according to claim 1, wherein in each case a
temperature and/or a current is ascertained as the first and the
second measured value.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. .sctn.
119(a) of Europe Patent Application No. 19161181.3 filed Mar. 7,
2019, the disclosure of which is expressly incorporated by
reference herein in its entirety.
BACKGROUND
1. Field of the Invention
The present invention relates to a method for controlling a
long-stator linear motor, a first measured value being ascertained
in a first measurement section and a second measured value being
ascertained in a second measurement section, in each case along a
transport path in a movement direction.
2. Discussion of Background Information
A long-stator linear motor (LLM) comprises a plurality of electric
drive coils which form one or more stator(s) and are arranged next
to one another in a stationary manner on one side, two sides or
more than one side along a transport path. Furthermore, a number of
excitation magnets are each arranged on transport units as
permanent magnets or as an electrical coil or as a short-circuit
winding. The magnets are usually attached to the transport unit on
one side, two sides or more sides in the movement direction such
that they can interact with the drive coils of the stator. The
long-stator linear motor can be in the form of a synchronous
machine, both self-excited or externally excited, or in the form of
an asynchronous machine. Owing to the interaction of the
(electro)magnetic fields of the magnets and the drive coils, a
propulsive force acts on the magnets of the transport unit, which
in turn moves the transport unit in the movement direction. This is
done by activating the individual drive coils to adjust the
magnetic flux, which influences the amount of the propulsive force.
Long-stator linear motors are increasingly being used as a
replacement for conventional continuous conveyors or
rotary-to-linear translation units (e.g. rotary motor on conveyor
belt, transmission belts or chains) in order to meet the
requirements of modern, flexible logistics units. A transport unit
must, of course, be guided along the transport path and held
thereon in a suitable manner. Any given guide elements of the
transport units can interact with guide elements of the transport
path; for example rollers, wheels, sliding elements or guide
surfaces can be used. These guide elements can also be arranged on
one side, two sides or more sides. In order to adjust the positions
of the transport units on the stator, an actual position is of
course also required in addition to a target position. The device
for detecting the actual position and for specifying the actual
position can be integrated into the long-stator linear motor or can
also be implemented external.
The position, speed and acceleration of the transport units or
another physical quantity of the entire transport path can be
ascertained as a whole. This can be interpreted in such a way that
a measurement section is provided which covers the entire transport
path. A measurement section comprises one or more measuring sensors
for detecting a measured value. Each measured value represents an
actual value of a physical quantity. For example, a position of a
transport unit in the measurement section can be determined as a
measured value, by means of which the actual position is
represented as a physical quantity. This can be done directly in
the measurement section by means of position sensors. Position
observers, which determine the position based on other information
such as voltages and currents, can also be provided.
If only one measurement section is thus provided, the transport
path can only have a one-dimensional topology, i.e. a concentricity
or a line. The transport path can then accordingly not comprise any
switches, since the measurement section would otherwise have to
overlap itself. In contrast, the transport path of a long-stator
linear motor can also be assembled from a plurality of measurement
sections. Usually, but not necessarily, each measurement section
covers one transport segment or part of a transport segment. A
transport segment denotes a modular section of the transport path
and comprises a number of drive coils. The measurement sections are
usually spaced apart from one another along the transport path in
the movement direction or are arranged adjacent to one another.
In order to ascertain a global actual position of a transport unit,
the measurement section at which a transport unit is located in
each case can first be ascertained. Furthermore, an actual section
position on the relevant measurement section can be ascertained.
The individual actual section positions are merged into a global
actual position on the transport path. This enables the transport
unit to be assigned a unique global actual position, for example in
relation to a selected reference point. If the measurement sections
together cover the transport path of the linear motor completely,
the transport units can be assigned a unique actual position in
relation to an (arbitrary) reference point at any time. This is
called a complementary sensor data fusion, and is known for example
from U.S. Pat. No. 6,876,107 B2. The individual measurement
sections complement one another and are arranged side-by-side
without gaps.
SUMMARY
The problem addressed by the present invention is that of improving
the control of the long-stator linear motor.
The problem is solved according to the invention by the first
measurement section overlapping, in an overlap region in the
movement direction, the second measurement section, the first
measured value and the second measured value representing the same
actual value of a physical quantity and an operating parameter of
the long-stator linear motor being determined based on a deviation
occurring between the first measured value the second measured
value.
By overlapping the measurement sections, redundant measured values
are generated in the overlap region. The relevant measured value
can be ascertained or observed in the associated measurement
section by a sensor, or also by the interaction of sensors in the
relevant measurement section. It is determined whether and to what
extent the first measured value of the first measurement section
deviates from the second measured value of the second measurement
section, it being of course possible for a tolerance to be
provided. If a deviation occurs, it is used to determine an
operating parameter. The first and/or the second measured value can
be used to determine the operating parameter. The first and the
second measured value themselves have to represent only the
physical quantity. This does not mean that the measured values must
directly constitute the same physical quantity. For example, the
first measured value can directly describe an actual position and
the second measured value can describe a current, from which in
turn the actual position is determined. Thus, the first measured
value directly represents the actual position as a physical
quantity and the second measured value indirectly represents the
actual position as a physical quantity.
Of course, the method according to the invention is not limited to
two measured values of which each comes from an associated
measurement section. One measured value each from more than two
overlapping measurement sections can also be used to ascertain the
operating parameter, or also a plurality of measured values from
two or more overlapping measurement sections.
The measurement sections can be provided on opposite sides of the
transport path.
Although this results in an overlap region when viewed in the
movement direction, the measurement sections can be arranged at a
distance from one another in a direction transverse to the movement
direction. Such arrangements can be found in particular in
long-stator linear motors having double combs. Double-comb
long-stator linear motors are characterized by two drive sides
arranged along the transport path, one stator being provided per
drive side. Drive coils are thus arranged on each side.
Accordingly, excitation magnets are provided on both sides of a
transport unit, each of which magnets cooperates with the drive
coils on one side.
The measurement sections can also be provided on the same side of
the transport path.
The configuration can be provided in which the sensors of two
measurement sections are arranged so as to overlap in the movement
direction. However, the sensors associated with the respective
measurement sections are often arranged so as not to overlap.
Nevertheless, the measurement sections indicate the visual range of
the sensors and not the physical extent of the sensors themselves.
In general terms, overlapping measurement sections mean an overlap
of the fields of view of the sensors, it being possible for the
sensors themselves to also overlap. Of course, this also applies to
measurement sections that are arranged on opposite sides of the
transport path.
Of course, a plurality of measurement sections can also be arranged
along a transport path such that there is a mixture of overlap
regions on opposite sides and on the same side of the transport
path. A third measured value from a third measurement section can
also be compared with the first and the second measured values or
further measured values from further measurement sections, etc.
An approximation of the actual value is advantageously determined
as the operating parameter.
This approximation can of course be carried out over the entire
overlap region for occurring actual values, a first and a second
measured value being used for the respective actual values.
The first or the second measured value can be selected as an
approximation of the actual value.
This corresponds to a selective process, which enables a
particularly rapid approximation of the actual value. This means
that even if one measurement section fails in the overlap region,
the other measurement section can continue to deliver measured
values, thus preventing failure of the entire long-stator linear
motor.
The first or the second measured value can be selected based on a
classification of the relevant measured value and/or an expected
accuracy of the respective measured values.
The first or the second measured value can be selected as an
approximation of the actual value based on an existing
classification of the measured value or of the measurement section.
For example, the measured value which can be assumed to be more
accurate due to the classification can thus be selected.
A selection of one of the measured values can also be made based on
the accuracy of the measured values. For example, it can be assumed
that the accuracy at the edge of an associated measurement section
drops, as a result of which the position of the determined measured
value in relation to the measurement section can be incorporated
into the selection of the measured value. A decrease in the
accuracy of the measured values with increasing distance between
the sensor and the measurement object can also be taken into
account in the selection as a geometry factor. In the case of
opposite measurement sections, the measured values from the
measurement section to which a transport unit is closer can be
selected, for example.
The selection of a measured value can also be made using learning
algorithms, such as neural networks.
As mentioned, the actual value of a physical quantity is
represented by measured values in both measurement sections. Since
there are two measured values, the actual value cannot be clearly
determined, as a result of which the measured values are preferably
processed in order to approximate the actual value. The actual
value can thus be determined with increased accuracy, since not
only one measured value from one measurement section, but measured
values from two (or more) measurement sections serve as the basis.
This is known as competing sensor data fusion. The actual value to
be selected can be determined based on an existing classification
of the measured value or of the measurement section. The actual
value can also be approximated, for example, by averaging the
measured values.
Advantageously, however, the first and the second measured values
are each provided with a weighting factor and the approximation of
the actual value is ascertained as the operating parameter from the
first and the second measured values and from the associated
weighting factor in each case.
In contrast to a selective method, one measured value is not
selected as an approximation of the actual value. Instead, both
measured values are taken into account, both measured values being
weighted in each ease. The actual value can be approximated even
better by using a weighting factor for the respective measured
values.
The weighting factor can also comprise a model factor, which is
determined by the magnitude of a deviation of the measured value
from a reference model.
The model factor can thus be determined based on a reference model,
it being possible, for example, for the model to represent a
physical behavior. For example, the equations of motion of a
transport unit can be used for the modeling and the deviation of
the real motion determined by the measured values can be
incorporated into the model factor. The greater the deviation
between a measured value and the model, the more likely this
measured value is incorrect. The model factor can be selected based
on this. This can occur in particular in opposite measurement
sections since although these overlap in the movement direction,
they can nevertheless be spaced apart from one another in the
transverse direction, which has a high probability of being able to
deliver different measured values.
The weighting factor can comprise a geometry factor, which is
determined by the position of the measured value in the measurement
section.
For example, it can be assumed that the accuracy of the measured
values at the edge of an associated measurement section drops, as a
result of which the position of the ascertained measured value in
relation to the measurement section can be incorporated into the
geometry factor. Measured values at the edge of the measurement
section are thus weighted less, for example, than measured values
in the center of the measurement section. A decrease in the
accuracy of the measured values with increasing distance between
the sensor and the measurement object can also be taken into
account as a geometry factor. In the case of opposite measurement
sections, the measured values front the measurement section to
which a transport unit is closer can be weighted higher, for
example.
The weighting factor can comprise a statistical factor which is
determined by a statistical distribution function.
The statistical factor can take into account, for example,
parameterized random distribution of the measurement signals, it
being possible for the variance of the measured values to be
estimated. This can be done in particular when determining the
actual position by assuming that the variance increases as the
distance between the magnetic plate of the transport unit and the
position sensor increases. This is particularly expedient in
combination with a geometric weighting factor.
The weighting factors can also be used by learning algorithms, such
as neural networks. Any combination of the factors and methods
mentioned can of course be used to determine the weighting
functions.
In each case, a measurement position of a transport unit on the
transport path can be ascertained as the first and the second
measured value.
The actual position as the actual value can thus be represented in
each case by the measurement positions as the measured values and
thus the control of the transport units can thus be improved since
the actual position can be determined more accurately by taking
into account the measured values from a plurality of measurement
sections.
Likewise, in each case a speed and/or an acceleration of a
transport unit on the transport path and/or in each case a
temperature and/or a current can be ascertained as the first and
the second measured value.
The occurrence of interference and/or an error and/or wear on the
long-stator linear motor can be determined as the operating
parameter from the deviation of the first and second measured
values.
If interference, an error or wear occurs, the first measured value
and the second measured value can deviate from one another over a
predefined tolerance. A corresponding deviation can thus be used to
deduce interference, an error or wear.
The measured values can be reliably detected and/or reliably
evaluated. "Reliable" can be defined according to a category in
table 10 of the standard DIN EN ISO 13849-1:2016-06 and thus,
depending on the safety category, single-fault safety, double-fault
safety, etc. can be provided.
An action can be triggered when interference, an error or wear is
detected. An emergency stop, the output of an (e.g. acoustic or
optical) signal, the setting of a flag, etc. can be carried out as
an action.
Mechanical assembly errors, but also failures (e.g. of a
measurement section due to a sensor error or a magnetic disk loss)
can be regarded as errors. It is also possible to ascertain
parameters that have been initialized incorrectly, for example an
incorrect definition of a measurement section, as a result of which
the measured value from said measurement section differs
accordingly from the measured value from an overlapping measurement
section.
Incorrect assembly of transport segments can lead to incorrect
positioning of a transport unit on the transport path, which can
interfere with higher-level processes, in particular the adjustment
of the positions or trajectories of the transport units. This can
result in discontinuous manipulated variables, unstable control
loops, overcurrent errors, contouring error truncations, etc. There
may also be occasions where control loops partially correct
themselves against one another, which in turn can create unstable
control loops and can also result in an increased energy
requirement. A deviation of the measured values in the overlap
region can be used to infer such incorrect assembly of transport
segments, in particular if each of the measurement sections covers
a transport segment.
Interferences such as environmental conditions (e.g. increased
temperature) can also be identified in the same way, since these
influence the measured values of the sensors of individual
measurement sections. Furthermore, the failure of a measurement
section or a part of a measurement section (sensor failure,
magnetic disk loss, . . . ) can be identified.
A deviation of the measured values can also be used to identify,
for example, wear on guide elements, such as rollers, in particular
in the case of measurement sections positioned opposite one
another. A change in the distance of the moving parts from the
relevant measurement section can be identified based on different
measured values. In the case of deviating measured values from
overlapping measurement sections, this allows conclusions to be
drawn about one-sided wear of the guide elements (e.g. rollers),
magnetic disk loss, demagnetization of a magnetic disk, sensor
malfunction (e.g. sensor drift).
It can also be ascertained on which side the transport unit has a
smaller distance from the transport path. This can also occur, for
example, by means of one-sided wear. This information can be used
for targeted actuation of the drive coils on the side having the
smaller distance, as a result of which energy can be saved and
losses that occur can also be reduced.
Other exemplary embodiments and advantages of the present invention
may be ascertained by reviewing the present disclosure and the
accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is described in greater detail below with
reference to FIG. 1 to 2B, which show advantageous embodiments of
the invention by way of example in a schematic and non-limiting
manner. In the drawings:
FIG. 1 shows a long-stator linear motor;
FIG. 2A shows two measurement sections on the same side of the
transport path; and
FIG. 2B two measurement sections on opposite sides of the transport
path.
DETAILED DESCRIPTION
The particulars shown herein are by way of example and for purposes
of illustrative discussion of the embodiments of the present
invention only and are presented in the cause of providing what is
believed to be the most useful and readily understood description
of the principles and conceptual aspects of the present invention.
In this regard, no attempt is made to show structural details of
the present invention in more detail than is necessary for the
fundamental understanding of the present invention, the description
taken with the drawings making apparent to those skilled in the art
how the several forms of the present invention may be embodied in
practice.
FIG. 1 shows a long-stator linear motor 2, the stator of the
long-stator linear motor 2 being, by way of example, in the form of
a closed transport path 20. A plurality of drive coils L are
arranged one after the other on the transport path 20 in the
direction of movement r of a transport unit 1, each of which coils
is energized in normal operation under the control of a control
unit R at a coil current i.sub.m in order to generate a moving
magnetic field. The coil current i.sub.m through the respective
drive coils L can be fundamentally different from drive coil L to
drive coil L. The control unit R can be in the form of suitable
hardware and/or in the form of software running on suitable
hardware. The drive coils L arranged next to one another in the
movement direction r are arranged on the transport path 20 on a
stationary support structure 3 (only implied in the drawings).
Depending on the application and as needed, the transport path 20
can have any shape, and can comprise closed and/or open path
sections. The transport path 20 can lie in one plane, but can also
be guided in space as desired.
A transport path 20 usually consists of a plurality of assembled
transport segments, each having a number of drive coils L.
Likewise, switches can also be used to guide a transport unit 1
from a first transport segment 20 to a second transport
segment.
A transport unit 1 must, of course, be guided along the transport
path 20 and held thereon in a suitable manner. Any given guide
elements of the transport unit 1 can interact with guide elements
of the transport path 20, it being possible to use rollers, wheels,
sliding elements or guide surfaces, for example. These guide
elements can also be arranged in sections on one side, two sides or
on more than one side.
Measurement sections 21, 22 are arranged along the transport path
20 of the long-stator linear motor 2, each measurement section 21,
22 extending over part of the transport path 20. A measurement
section 21, 22 can extend over a plurality of successive transport
segments, or can also be limited to only one transport segment. Of
course, a measurement section 21, 22 can also protrude beyond a
transport segment or be considered independently of transport
segments. For this reason, measurement sections 21, 22 and not
transport segments are considered in the present description. For
reasons of clarity, the measurement sections 21, 22 are not
indicated in FIG. 1. Instead, part of the transport path 20 is
considered in FIGS. 2A and 2B, overlapping measurement sections 21,
22 being shown in each case.
A measurement section 21, 22 is designed to ascertain one or more
measured values m1, m2, each measured value m1, m2 representing an
actual value X of a physical quantity G. An actual position x
and/or an actual speed v and/or an actual acceleration a of a
transport unit 1 can be considered to be the physical quantity G. A
measured value m1, m2 thus constitutes a measurement position, a
measurement speed or a measurement acceleration, and thus
represents an actual position x, an actual speed v, or an actual
acceleration a, it not being necessary for both measured values m1,
m2 to directly constitute the same physical quantity G, but only to
represent said quantity.
If an actual position is ascertained as the physical quantity G,
this can be done with reference to a reference point, it being
possible for the reference point to be assumed at a measurement
section 21, 22, a transport segment or any other point in space.
Other physical quantities G, such as a prevailing force, a flowing
current or a prevailing temperature can also be represented by the
measured values m1, m2. From this, a physical quantity G, such as
an actual position x, can in turn be calculated, which can also be
carried out by an observer.
A first measured value m1 can also directly represent a physical
quantity G, for example the actual position. This means that the
first measured value m1 constitutes the actual position itself. A
second measured value m2, in contrast, can constitute a different
physical quantity, for example an electric current, from which the
actual position is represented as the physical quantity G. The
first measured value m1 thus describes the physical quantity G
directly and the second measured value m2 describes the physical
quantity G indirectly. However, both measured values m1, m2
represent the physical quantity G.
Magnetic field sensors, for example Hall sensors or
magnetoresistive sensors can thus be provided as sensors. However,
the sensors can also use other physical measurement principles,
such as optical sensors, capacitive sensors or inductive sensors.
Current sensors which determined the coil current i.sub.m through a
drive coil L can also be provided. As is known, a normal force
and/or propulsive force acting on a transport unit 1 can be
determined from the coil current i.sub.m. A temperature sensor can
also be provided as the sensor.
A first and a second measurement section 21, 22 are shown by way of
example in FIG. 2A. According to the invention, at least two
measurement sections 21, 22 have an overlap region B in the
movement direction r, i.e. along the transport path 20. The
measurement sections 21, 22 overlapping in an overlap region B can
be arranged on the same side of the transport path 20 as in FIG.
2A, or also on opposite sides of the transport path 20, as shown in
FIG. 2B.
In both cases shown, a first measured value m1 in the first
measurement section 21 is ascertained in the overlap region B and a
second measured value m2 in the second measurement section 22 is
ascertained in the overlap region B. Both measured values m1, m2
represent the same actual value X of a physical quantity G. For
example, an actual position x of a transport unit 1 can be
represented as an actual value X by the first measured value m1 of
the first measurement section 21. Analogously, the actual position
x of the transport unit 1 can also be represented as the actual
value X by the second measured value m2 of the second measurement
section 22, i.e. as the second actual measurement position.
Only one actual value X is shown in FIGS. 2A and 2B, but of course
other and/or further actual values X can also be ascertained in the
overlap region B, measured values m1, m2 which represent the
other/further actual values X being determined in each ease.
If the first measured value m1 and the second measured value m2
differ, then an operating parameter P of the long-stator linear
motor 2 can be determined from the deviation of the first measured
value m1 from the second measured value m2, which gives the
operating parameter P as a function of the measured values P=f(m1,
m2).
This takes place in FIGS. 2A, 2B by way of example in a processing
unit V, but can instead of course also take place in the control
unit R or another unit already present on the long-stator linear
motor 1, for example. The operating parameter P can also be output
and/or processed, for example in order to control the transport
units 1.
An approximation of the real actual value X can be determined, for
example, as the operating parameter P from the deviation of the
first and the second measured value m1, m2. This can be done by the
measurement sections 21, 22 being transformed into a common
coordinate system. The measured values m1, m2 can be averaged or
can each be assigned a weighting factor f1, f2, which in each case
gives the operating parameter P as a function of the measured
values m1, m2, and the associated weighting factor f1, f2: P=f(m1,
f2; m2, f2). An approximation of the actual value X can be
ascertained as the operating parameter P. A weighting factor f1, 12
of a measurement section 21, 22 can be initially defined and/or
adjusted over time.
The relevant measurement section 21, 22 can also contain regions of
different measuring accuracy, it being possible for the measuring
accuracy to be able to change discretely and/or continuously over a
measurement section 21, 22 or part of the measurement section 21,
22. Likewise, the measuring accuracy of a measurement section 21,
22 can change over time and/or depending on other influences such
as temperature, contamination and/or aging of the sensors. The
relevant weighting factor f1, f2 can comprise a geometry factor
which is determined by the position of the measured value m1, m2 in
the measurement section 21, 22. For example, accuracy depending on
the position on the measurement section 21, 22, the distance from
the measurement object, the temperature or magnetic stray fields
can be incorporated into the geometry factor. If the accuracy of
the measured values m1, m2 decreases toward the edge of the
measurement section 21, 22, the geometry factor can be used as a
function of the distance from the center of the measurement section
21, 22.
Of course, a weighting factor f1, f2 can vary depending on the
position of the measured value in relation to the measurement
section 21, 22, which can also be achieved by a geometry
factor.
The weighting factor f1, f2 can also comprise a statistical factor
which is determined by a statistical distribution function. If the
probability distributions of the individual measurement sections
21, 22 are known, independent of one another, normally distributed
and have the same average value, a maximum likelihood estimator
which uses weighted least squares can be used. The variance on a
measurement section 21, 22 can be a function of both time and
position on the measurement section 21, 22.
Model factors can also be incorporated into the weighting factors
f1, f2. The Kalman filter is mentioned as an example of a
model-based estimator. When designing a Kalman filter, assumptions
can also be made about the probability distribution of the measured
values m1, m2.
The first or the second measured value m1, m2 itself or an average
value of the first or of the second measured value m1, m2 could
also be selected as an approximation of the actual value X. The
information mentioned above in the context of the weighting
factors, which information is incorporated into the statistical
factors and/or geometry factors, can equally be used for the
selection of a measured value m1, m2 as an approximation of the
actual value X.
The occurrence of interference and/or an error and/or wear on the
long-stator linear motor 2 can be determined as the operating
parameter P from the deviation of the first and the second measured
value m1, m2. This is possible if the measured values m1, m2 of
overlapping measurement sections 21, 22 deviate from one another
due to the interference, or the error, or the wear. By implication,
the interference or the error or the wear can be inferred. For
example, the nature of the interference, the fault or the wear can
be inferred based on the magnitude of the deviation. Changed
environmental conditions, such as an increased temperature, can
also be regarded as interferences.
It is noted that the foregoing examples have been provided merely
for the purpose of explanation and are in no way to be construed as
limiting of the present invention. While the present invention has
been described with reference to an exemplary embodiment, it is
understood that the words which have been used herein are words of
description and illustration, rather than words of limitation.
Changes may be made, within the purview of the appended claims, as
presently stated and as amended, without departing from the scope
and spirit of the present invention in its aspects. Although the
present invention has been described herein with reference to
particular means, materials and embodiments, the present invention
is not intended to be limited to the particulars disclosed herein;
rather, the present invention extends to all functionally
equivalent structures, methods and uses, such as are within the
scope of the appended claims.
* * * * *
References